PCM location - how protected does it need to be?

[WorldsCrappiestTruck]

My first Gen3 LS I put the PCM behind the ashtray area, because I wanted a very clean engine bay - all the wiring is tucked and runs through a single 2” grommet in the firewall to the PCM. I LOVE how it looks under hood, less how it looks on the interior as you can see it up under the dash, and now I really dislike it because it’s going to really limit real estate for adding HVAC which I didn’t do up front (mistake - just wanted to get it going).

My current Gen3 I’d like to put the PCM under hood but hide it nicely. Maybe in the radiator support area on the lower drivers side? From the factory, these units were under the hood, strapped to a plastic mount and pretty much exposed to road grime, heat etc in the engine bay.

Is it okay to put it in a sealed box to “pretty” up an install, or should it have cooling airflow? Can you put it down in the water & dirt & grime as long as the unused pins have been silicone’d shut? Can it be protected from water, but should still have airflow around it?


Looking for creative recommendations to where you can “hide” a gen3 PCM underhood. Thx.

[LS short box]

Can't speak to where to hide the ECM in the engine compartment but the ECM is totally weather proof. My 98 Wrangler has a LS6/4L60E swap. Did it 16 years ago. It's my summer time around town cruiser. I plow my driveway with in the winter. Just did that last night. Zero issues with moisture.
ECM is mounted under the brake booster. Fuses/relays on the firewall. Pics.

[cj847]

On my swap I mounted the PCM on the inner fender behind the headlight, drivers' side. Not completely hidden, but no one notices it. Don't worry about dirt and water. That is where it is mounted on trucks from the factory.

[A1971Blazer]

This is before everything was assembled.
It's completely out of sight and adequately protected.
I also built an under-hood electrical fuse/relay box.
After the wiring was all done, I used black braided loom on all the wiring.
I practically disappears in the engine bay

[WorldsCrappiestTruck]

^^ that’s slick - I’d half-decided on that being the landing area for the electrical stuff.

[LS short box]

Pic of 68 C10 with a LS6 swap. I love to hide wires. For the front chassis harness I moved the fuse block back and behind left inner fender. Then filled the stock firewall hole. Ran the front and rear chassis harness along the frame rails.
The ECM wires behind the right cylinder head thru the fire wall.
No AC so the ECM and fuse block behind the glove box. I had to section the glove box a bit to make room.

[binford]

I would figure out you air cleaner setup first, as you might have to move stuff.
I ended up with a suburban air cleaner setup as I wanted the manual fan.

Mine is under the seat. I was going to mount it under the head light on the rad support, where the old voltage regulator use to be.